Gas discharge tube delay circuit



Jan. 4, 1938. R K. HONAMAN ET AL 2,104,128

GAS DISCHARGE TUBE DELAY CIRCUIT Filed Dec. 27, 1955 Short circuit removed at ,t -0.

Al l ml Ill IF I 1193-:

Input Circuit Input I Circuit wl l INVENTORS fi onamml zmfik -BY fiKSwant ATTORNEY Patented Jan. 4, 1938 PATENT OFFICE 2,104,128 GAS mscnaada ruin: DELAY cmcurr Richard Karl Honaman, Bloomfield, and Leland Kasson Swart, Mountain Lakes, N. L, assignors to-American Telephone and Telegraph Company, a corporation or New York Application December 27, 1935, Serial No. 56,395 9 Claims (Cl. 250-27) This invention relates to gas discharge tubes and to circuits therefor. This invention also relates to :delay circuits and to delay circuits employing gas discharge tubes.

5 In making measurements of induced voltages it becomes desirable to segregate surges of, for example, the 60 cycle type from short-lived tran-. sients due to lightning, static, etc., which may be imposed upon conductors and tend to interfere 30 with the accuracy of the measurements. These extraneous voltages, if of the character of lightning discharges, may be of such a wide range of amplitude and frequency as to render filtering 20 vide arrangements for; obtaining predeterminable and controllable time delays. The various methods and circuits for accomplishingthis objective may employ gas discharge tubes, condensers, resistors and sources of potential of such delay of any desired interval. 1

One of the features of this invention is based upon the fact that the delay interval may be determinedfrom the time required for a charged condenser to discharge through a resistor.

Another of the features of this invention is that the delay may be determined from the time required for a condenser in conjunction with a resistor to become charged to a predetermined J voltage.

Other and further objects and features of this invention will be better understood from the detailed description hereinafter following, when read in connection with the accompanying drawi0 ing in which Figure l illustrates-a circuit showing tion applied to circuits of hot cathode gas discharge tubes. I

Referring to Fig- 1 of the drawingf there is shown one method for producing delay. A condenser C is connected in parallel with a resistor R. and the parallel combination is connected to a battery B or other source of voltage as well as magnitudes and so arranged as to introduce ato a gas-discharge tube N. Assume that the gasdischarge tubeN is entirely shunted by a conductor, as shown in dotted lines. Then, in this assumed circuit, the condenser C will be charged to the voltage of the battery B.

If, now, the shunt around the tube N is opened or removed, the two electrodes of the tube N will be connected in series with the battery B and the resistor R-condenser C combination. The voltage across the tube will be zero at that instant 10 for the reason that the battery electromotive force and the counter-electromotive force across the condenser C will equal and balance each other. The condenser C will begin to discharge through the shunt resistor R. The potential 1 at the terminals oi the condenser will decrease exponentially at a rate determined by the constants of the condenser and resistor. At the same time, the potential across the terminals of the tube-which is the diiference between the battery potential and the condenser potential 20 will commence to rise logarithmically. When this voltage reaches the breakdown voltage of the tube N, the gas within the tubewill become ionized. Accordingly, a relay or other device (not shown in this figure) may then be operated 25 in a manner which will be apparent from the description of other circuits hereinafter following.

The elements just described form a circuit which operates according to some of the funso of condenser C in farads R the ohmic resistance of resistor R, E0 the voltage across condenser C, ET the voltage across the. terminals of tube N,- 5 the time tmay be considered to be zero and to start running upon the removal of the shunt cir cuit around the tube. The condenser 0 begins to discharge through the resistor R, starting with an initial voltagels. Then,

2 v The voltage across the tube is t r=Es-' c= s( Thus the voltage across the tube rises from zero at a rate given by (2). From (2) we get ffi= (a) and t E --E "F0 e 4) The expression (4) determines between ET and the time I: required to reach the voltage Er. Thus fi==o"43 log '(EB ET) If E1- is made equal to the breakdown voltage of the tube N, then the Equation (5) will determine the time t required to 'lonize the gas within the tube after the short-circuit around the tube is removed.

Thus, if tube N has a breakdown-voltage of 70 volts, for example, and the battery 13 is one of 135 volts, then 1 0.317 t- RC0.74RC

It will be clear, therefore, that the delay may be increased by increasing the capacity of the condenser C or by increasing the ohmic resistance of resistor It or by decreasing the voltage of battery B, These factors may be set at definite values and a circuit based thereon will produce delay with considerable accuracy. v

In Fig. 2, the relay R0 is in a signal or other circuit which applies current to the relay winding,

to initiateoperation of the system and delayed operation of relay R1. The armature of this relay R0 is connected to the cathode K1 of a three-element gas discharge tube No known as a cold cathode tube, the other cathode K1 of which is connected to the make-contact of relay Ra through a circuit which includes the battery or voltage generator B1 and the variable resistor Z1. The resistor Z2 is bridged across the cathodes K1 and K: of the tube No. The battery B1'is connected to the condenser C1 and the variable resistor Z; and supplies current for maintaining the condenser C1 in a continuously charged condition. This battery is of a voltage which exceeds that required to ionize the gas between cathodes K1 and K1 0! the tube No. When the relay R0 is unoperated, a circuit. will be established which will completely shunt not alone the resistor. Z: but also the cathodes K1 and K201 the tube No.

The anode A of tube No is connected in a' circuit which includes the winding of relay R2,

resistor Z1, the winding'of relay R1, battery or voltage generator B:, 'battery or voltage generator B1 and the cathode K: of tube No. It will be apparent also thatthe s'ources B1 and 32 may be but a single source or voltage, that is,a single battery and that it may be tapped so as to give the effect of the two separate sources shown. The

electrodes A and K: of tube No form a gap which is initially under the control of the gap between the cathodesK1 and K: ofthe tube. The relay R1 is a vibrating relay, vibrating continuously while the gas within tube No is ionizedin rethe relationship sponse to the application of sumo-lent voltage be- 1 1 tween the cathodes K1 and K2 and while in elements of resistance'Zs and capacitance C2,

the armature and contact of the relay R1 being connected across the circuit oi the electrodesA and K: through the winding of this relay.

Before relay Ro operates, the source B1 supplies charging current to the condenser C, over the circuit which includes the back contact and armature of relay R0 .and the variable resistor Z3.

This current charges the condenser G1 at a rate depending upon the magnitude to which the resistor Z3 has been previously adjusted. The

potentialof the source B1 exceeds that required to ionize the gas between the electrodes K1 and K2 of the tube No but by virtue of the shortcircuit around these electrodes formed by the armature and back contact of relay Ro, ionization between these electrodes of the tube is prevented. Under normal conditions, the battery B1 will charge the condenser C1 to a voltage ap proximately equal to the voltage of this battery and after the condenser C1 charged practically no current will traverse resistor Z3.

After the relay R0 operates in response to the flow of sufiicient current through its winding, the resistor Z1 becomes connected to the circuit and provides a discharge path for the condenser C1, this discharge oath including both resistors Z1 and Z1 and the armature and make-contact of the relay R0. The discharge current depends upon the combined resistance of resistors Z1 and 2a. The operationof the relay R0 at the same time removes the' shunt circuit around both resistor Z2 and the cathodes K1 and K1 oi the tube No. Some time after the operation of f relay R0, the condenser C1 will become discharged to a voltage which, when combined with that-of the battery B1, will equal the voltage required to ionize the gas between the cathodes K1 and K2 of the tube No. Assuming the battery B1 to be of 90 volts and the ionization potential between cathodesflK1 and K2. to be volts, the ionization potential will be reached when the condenser has been discharged to a voltage of approximately 20 volts. When this lower potential across the condenser C1 is reached, the impedance between the cathodes K1 and K1 will be reduced to a negligible value andallowing current to pass between electrodes Aand K2 of the tube. The batteries B1 and B2 will then drive current through the circuit which includes the winding of relay R1, the resistor Z1, the winding of relay R1, and between electrodes A to K1 of the tube No. ated as'long as the voltage between the cathodes K1 and K2 exceeds the value required for ionization. Upon theoperation of therelay R1, however, the armature and contact of this relay will shunt the circuit containihg the electrodes A and K2 of the tube and the winding 'of relay' R1. This will promptly delonize the gas between erated, again shunting the circuit between the The relay R1 will operate and remain oper-.

becomes fully in the tube N0 only after the condenser C1 has become discharged to a suiiiciently low value. No relay winding or other inductive element is included in the circuit of the cathodes K1 and So, it will be seen that the operation of the relay R0 removes the shunt around the circuit of the electrodes K1 and K2 a predetermined period of time after the operation of the relay R0 and effects the operation of the work circuit of relays R1 and R2. If, perchance, the operation ofthe relay R0 is interrupted before the condenser C1 has discharged to the required low value, the gap K1 and K2 will not become ionized and the work circuit will then not be operated. Hence, if the relay R0 is operated merely by virtue of some transient effect such as a lightning surge, it will be impossible to bring about the operation of the work circuit of the arrangement in response' to that surge. But, where the relay R0 remains operated longer than the time required. to sufiiciently discharge condenser C1, the work circuit will be operated for a period of time which will closely match the period in which the relay R0 remains operated, less the time for discharg ing the condenser.

In Fig. 3, the cathodes K1 and K2 of the tube N0 are connected to the biasing source of potential B1 through a parallel circuit comprising condenser C2 and resistor Z0. The relay R0 is normally unoperated and its armature and back contact bridges the resistor Z1 across the gap K1-K1. The resistor 21' is one of low magnitude while the resistor Z0 is one of large magnitude.

The condenser C1 becomes charged by the battery 131 through the circuit of resistor Z1 and the armature and back contact of therelay R0. The voltage across the condenser will approximate that of the 'battery.B1 and therefore there will be no eifective potential across the resistor Z1 or across the gap K1-K1. After the relay R0 operates, however, the shunt resistor Z1 will be effectively removed from the circuit and the condenser C2 will discharge through the resistor Z0. At a predetermined interval after this dis charge has started-an interval determined by the capacity of the condenser C2, the magnitude of the resistor Z0 and the time required to discharge the condenser toa potentialof predetermined low orderthe difference between the potentials of the battery B1 and that across the condenser C1 will equal the ionization voltage of the gap K1Kz of the tube. Ionization will then which is less than occur and the batteries B1 and 30 will then send current through the circuit of the winding of the relay R3, and electrodes A and K1 of the tube N0, and the relay Ra will operate and remain operated as long as the relay R0 has operated. No deionization circuit has been shown for the anode or work circuit of the tube but any deionization circuit may be used in this arrangement.

If, however, the relay R0 operates for an interval that required to sufliciently discharge the condenser C2, the gas within the tube N0 will not become ionized and the work circuit of relayRs will not be operated.

Fig. lahows a delay circuit of a somewhat diftube N1 are connected to the input circuit through a current-limiting resistor Z10 and a portion of the. battery B3 employed for biasing purposes.

The anode A of the tube is connected to the cathode K: through a circuit which includes the winding of relay R10 and the battery B3. The armature and back contact of the relay R 0 furnishes a circuit for completely shunting the gap formed by the cathodes K1 and K: of the tube N0. The anode 'A of the tube N2 is connected to the cathode K: through the winding of the relay R11 and the battery B3. The condenser C10 is 1 ferent type. Here the cathodes K1 and K: of the normally charged to the voltage determined, by V the lower tap and the right-hand terminal of the battery E3, the charging circuit including the armature and back contact of the relay R10, and

this condenser is shunted by a resistor Z11 which is of large (and variable) magnitude.

After a sufficiently high potential has been applied to the input circuit of the arrangement shown in Fig. 4, the gas between the gaps K1 and K2 of the tube N1 will become ionized as will the gap between the anode A and cathode K2 of tube N1 and the relay R10 will operate, the current for the relay operation being supplied by the battery B3. As the armature of the relay R10 leaves its 'back contact, the shunt around the gap-K1-Ka of the tube N2 will be removed. The condenser C10 will at the same time begin to discharge through the resistor Z11. As the voltage across the condenser C1 becomes reduced to a value such that the diflerence between that voltage and the voltage between the lower tap and right-hand terminal of the battery B3 approximates the voltage required to ionize the gas of the gap K1-Kz of the tube N2, the gas within the latter tube will become ionized and current will then flow through the winding of relay R11 and through electrodes A and K: of tube N2, the current for the latter operation being also supplied by the battery B3. The delay in the operation of relay R11 is determined by a number of factors, some of which are the capacity'of the condenser C10, the magnitude of the resistor Z11 and'the voltages to which the condenser C10 is normally charged and must be thereafter discharged to ionize the gas within the tube N2. Of course, if the input circuit of the system is supplied with a transient voltage or surge of extremely minute duration, the surge may be of too short duration to allow the condenser C10 to become sufficiently discharged and, of course, the relay R11 will therefore remain unoperated. No deionization circuit has been shown for either of the tubes of this arrangement but such deionization circuits as are-well known in the art may be employed for this purpose.

Fig. 5 shows a delay clrc'uitas part of an arrangement including hot-cathode tubes N11 and N12. One side or the input circuit is connected to B31 supplies current to the heaters of both tubes N11 and N12. The anode of the tube N11 is connected to the cathode by a series path which includes the winding of the relay R30 and the battery Baa. The armature and back contact of the relay R00 are in a circuit which connects the battery Bar to the condenser C30 and this circuit maintains the condenser C30 normally charged. The condenser C30 is shunted by a resistor Z31 and it is also connected between the grid and has happened. But, after the gas within the tube cathode of thetube N12 by means 01' the battery B30. The anode of the tube N1: is connected to the cathode of this tube by a path which includes the winding oi the relay R31 and the battery B32.

Ionization of the gas within the'tube N1: can only .occur after the condenserCao hasbecom discharged to a sufficiently low value and, of

course, the relay R31 cannot operate until this N11 has become ionized in response to application of suiiiciently high voltage to the input circuit, the relay R30 will operate and as the armature of the latter relay leaves its back contact, the'condenser C30 will be disconnected from its charging circuit. Discharging at a rate determined by the magnitude of the resistor Z31, the condenser C30 will ultimately reach a voltage which will be so far below the voltage of battery B30 that ionization may then take place in the grid circuit of the tube N12. When this occurs, the relay R31 will ope'rate'and remain operatedas long as sufllcient voltage continues to be appliedto the input cir- .tion may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

state of charge-of the i work circuit.

What is claimed is:

l. The combination of a three-electrode gas discharge tube, a condenser, a source of potential connected in series with the condenser and two of the electrodes of the tube, the potential of said source being greater than that required to ionize the gas between said two electrodes, a work circuit connected between the third electrode and one of the other "electrodes, and means for varying the 2. The combination of a'condenser, a gas discharge tube having first and second gaps, a source of potential the magnitude of which exceeds the ionization voltage of the first gap, means for connecting said source to the condenser for charging the condenser to the voltage oithe source, said source and said charged condenser being con-- nected in opposition and to the first gap-oi the tube, means Iorslowly discharging the condenser for thereafter ionizing the gas within the first gap, and a load circuit connected with the second gap and operated in response to the ionization oi the gas within the first gap.

'3. A delay circuit comprising a normally deionized gas discharge tube, a condenser, a source condenser to operate the 9,104,128 01' Voltage connected in series with said condenser and with the electrodes of said tube, a circuit oi negligible resistance in shunt. with the electrodes oi said tube, a resistor in shunt with said condenser, and means for ionizing the gas within the tube, saidmeans including means for opening the circuit of negligible resistance in shunt with the tube.

4. The combination of a gas discharge tube, a capacitive element, charging means connected in series with said capacitive element and with the electrodes of said tube, means for preventing ionization of the gas within the tube, means for uncoupling the ionization preventing means from the tube, and means for discharging the capacitive element.

5. The combination of a condenser, a source of potential, a gas discharge tube connected in;

series with said condenser and said source, and

means for charging the condenser to a predetermined voltage, said predetermined voltage at charge and that of said source being together equal to the ionization voltage of the tube.

6. The combination of a source of potential, a condenser charged to the potential of said source. a gas discharge tube having an ionization potential below said potential, said tube being connectedto said source and said condenser so that their potentials mutually oppose each other, and means for reducing the potential across the condenser to a point such that the diiierence between the potential across the condenser and that of the source equals the ionization potential of the tube.

'7. The method of delaying the operation oi a circuit dependent upon the ionization of the gas within a gas discharge tube which consists in producing a fixed and substantially invariable voltage, charging a condenser to a counter-voltage approaching said fixed voltage, slowly discharging thecon'denser, and ionizing the gas within the tube when the ,voltage across the condenser is reduced below-said fixed voltage by a mode-- termined amount. r

8. The method of producing delay with a gas tube which consists in shunting the tube out of circuit, charging a, condenser to a voltage exceeding the ionization voltage of the tube, removing the shunt around the tube, and discharging the condenser in series with a source of voltage to a voltage together approximating the ionization voltage of the tube.

9. The method of operating a gas discharge tube which consists in charging a condenser to a voltage exceeding the tube breakdown voltage,

opposing. the voltage of the'c'ondenser by an equal voltage, discharging the condenser to a progressively lower voltage and operating the tube when the voltage of discharge diflers from the opposing voltage by an amount corresponding to the tubes breakdown voltage.

RICHARD KARL HONA MAN. LELAND KASSON SWART. 

